Definition of Deerfly fever

Deerfly fever: An infection in rabbits and other wild rodents caused by the bacterium Francisella tularensis that can be transmitted to humans by contact with infected animal tissues or ticks. Also called tularemia.

The main mode of transmission to humans is tick bites in the summer and exposure to rabbits in the fall and winter during the small-game hunting season. The domestic rabbit is the main source of serious infection. Transmission may be by direct contact, contact with aerosolized bacteria, eating infected tissue or by the bite of a colonized tick, deerfly, or flea that has fed on a sick rabbit.

Symptoms include a red spot on the skin enlarging to an ulcer, enlarged lymph nodes (swollen glands) in the groin or armpits, headache, muscle pain, shortness of breath, fever, chills, sweating, weight loss, and joint stiffness. Some people develop an atypical pneumonia. The illness may continue for several weeks after the onset of symptoms.

The antibiotics streptomycin and tetracycline are commonly used to treat tularemia. (Oral tetracycline is usually not prescribed for children until after all the permanent teeth have erupted. It can permanently discolor teeth that are still forming.)

A vaccine is available for people at high risk (trappers, hunters, and laboratory workers) to prevent the disease.

Tularemia is fatal in about 5% of untreated cases, and in less than 1% of treated cases. Possible complications include meningitis, pneumonia, pericarditis and osteomyelitis.

Tularemia has declined in frequency in the US, probably because wild rabbits are no longer available in markets and also because of increased awareness among hunters of the risks posed by sick rabbits.